Video disc styli are generally fabricated out of single crystal dielecric support materials such as diamond or sapphire (.alpha.-Al.sub.2 O.sub.3). When a capacitive playback system is used, with either a grooved or non-grooved video disc, the stylus dielectric support material is coated on at least one surface with a conductive metal layer. If a pressure pickup playback system is utilized, then at least one surface of the stylus dielectric support material is joined to a piezoelectrical material.
U.S. Pat. No. 3,842,194 of Clemens discloses a video disc having a playback system utilizing variable capacitance. In one configuration of the Clemen's system information representative of recorded picture and sound is encoded in the form of a relief pattern in a relatively fine spiral groove on the surface of a disc record. For example, groove widths of about 3.5 micrometers and groove depths of about 1.0 micrometer may be used. During playback a pickup stylus about 2.0 micrometers wide having a thin conductive electrode thereon, for example, about 0.2 micrometer thick, engages the groove as the record is rotated by a supportive turntable. Capacitive variations between the stylus electrode and the disc record surface are sensed to recover the pre-recorded information. In systems of the above type, the use of a relatively fine record groove and groove engaging requirements for the pickup stylus results in a stylus tip which is extremely small. Another capacitive playback system does not utilize grooves but relies on signals recorded in the disc record to keep the stylus in its proper position.
In U.S. Pat. No. 4,104,832 of Keizer, a method is disclosed whereby a pyramidal-shaped support element is shaped by an abrasive lapping disc to form a capacitive video disc stylus having a novel keel-tipped structure. The keel-tipped pickup stylus comprises a dielectric support element having a tapered body, a constricted terminal portion and shoulders interconnecting the body with a constricted terminal portion.
With the presently available stylus materials such as diamond and sapphire, properties such as ease of fabrication, cost of materials, usable life of the stylus, adherence of a conductive layer to the stylus surface and compatibility with the disc surface must be balanced. It would therefore be desirable to have an alternate choice of stylus material which may result in a better balance of these properties to produce a more desirable playback stylus.